Why Bigger Bumblebees Are Early Risers

There’s an advantage to being an earlier riser. For bumblebees, heading out early in the morning means they have more time to forage and fewer competitors for the best pollen.

There are also disadvantages to flying in the dim, morning light. Flying at dusk increases their chances of getting lost or of getting snatched by a predator.

But larger bumblebees are willing to make those tradeoffs, a new study, published in the journal Ecology and Evolution, finds.

Researchers tracked foraging bumblebees of all body sizes for five days and found that bigger bees exited the hive for the first time in the morning in dimmer conditions than smaller bumblebees.

Tracking Trips Around the Hive

For the study, researchers obtained 17 colonies of buff-tailed bumblebees (Bombus terrestris) from a commercial breeder. They tested them in two locations in England.

“​We attached RFID tags, similar to those in contactless debit cards, to the thorax of the bee and then when they left and entered the nest the tag was scanned and logged,” lead author Katie Hall, a Ph.D. student at the University of Exeter, tells Treehugger.

One colony was tested at a time, placed in a small box, which was then put inside a large wooden box inside a room. There was a mix of vertical and horizontal tunnels that the bees could take to reach the one exit tunnel to get outside. Once outdoors, the bees either had access to a mix of urban gardens in one location or a rural agricultural landscape with hedges in the second location.

Each time the bees came into or out of the hive, they were scanned and the researchers tracked what time and how often they moved.

They found that the biggest bees and the most experienced foragers—which the researchers measured by the greatest number of trips they made to the outdoors—were the most likely to leave the hive in low light.

Benefits and Risks

Anatomy plays the main role in why the larger bees are able to navigate in less-than-ideal circumstances.

“​Larger bumblebees have bigger eyes than smaller bees and can therefore see better in low light,” Hall says. “Bumblebee vision is crucial for navigation, finding flowers, and getting home.”

Some flowers open at dawn or release nectar when the majority of pollinators aren’t even stirring yet. That gives the early risers an advantage.

“The benefits are that they can get to the untouched food resources before competitors,” Hall says. “However there is an increased risk of predation, getting lost, and hypothermia.”

The risks were even greater for smaller bees, which is why they typically stayed in the hive until the light was brighter

“​Smaller bees have smaller eyes than bigger bees and therefore they can not see as well,” Hall says. “Therefore in low light conditions, their risk of predation and getting lost is higher than larger bumblebees.”

These findings are important, researchers say, because it's important to understand why these critical insects act the way they do and what influences their behavior.

“Bees are vital both ecologically and economically. They pollinate wild flowers and a huge variety of crops. Therefore it is important to understand their behaviour,” Hall says. “This research is the first step in understanding the natural activity behaviour in dim light.”

More research should build on this work, she says, to see what impact noise pollution at night has on bumblebees.

Hall says, “Artificial light at night is increasing across the world and has been shown to disrupt natural light regimes and have significant impacts on the natural world.”